Semiconductor defects may include structural flaws, residual process material and other surface contamination, which occur during the production of semiconductor wafers. Defects can be introduced to a wafer at any process step in wafer production. For example, a particle defect may originate from contamination during a deposition process or it may be introduced to the wafer due to exposure during a wafer transfer from one process chamber to another. As another example, a scratch defect may occur due to abrasive polishing during a chemical mechanical planarization process, or it may occur due to faulty cleaning process or it may occur from operator error during wafer handing. Since defects can have a similar appearance but originate from different process steps, it can be difficult to find root causes of the defects, such as a faulty process. It is also important to know where the defect is located with respect the different process layers of the semiconductor wafer, which may also aid determination of the root cause of the defect.
To help detect and locate defects, a class of instruments called inspection tools is used. Inspection tools inspect the wafers at various critical points between process steps in wafer production. Such instruments scan wafer surfaces using a variety of techniques and detect and record the location of anomalies. Typically, these techniques involve directing a light or electron beam towards the surface of the semiconductor where the defect is, and detecting the resultant light reflected off or electrons emitted from the sample. The reflected light or emitted electrons may then be used to generate a target image of the surface of the semiconductor. Differences between the target image and a reference image (which is known to contain no defects) are determined and, when the differences are above a predetermined threshold, it may be determined that a defect exist.
One problem that occurs with existing inspection technologies is they do not always accurately locate where the defects are in relation to the different layers of the semiconductor. This is because many inspection tools collect one or two dimensional images of defects. For example, most electron beam inspection tools detect emitted electrons using one detector at one angle in relation to the sample surface. The data is collected from one perspective and results in a one dimensional representation or, at best, a flat two dimensional image, much like a common camera photograph. The one and two dimensional representations alone do not show depth. When viewing the image, one may not be able to distinguish between an indentation that recesses below the wafer surface and a bump or particle that protrudes above the wafer surface. If the defect is particle, it may occlude or shadow another defect behind it. Also, one will not know if the defect simply lies on the surface, extends into other process layers or spans over multiple layers.
The spatial location of defects can be vital information for engineers to accurately determine the root causes of defects. For example, if a particle is introduced in a deposition chamber during a deposition process, the particle may be embedded with the material of the deposition process layer. Whereas, if the particle was introduced after the deposition process, the particle will likely not be embedded within the material of the particular deposition process layer but rather reside on top of the wafer surface or within another process layer besides the particular deposition layer. Likewise, it is important for engineers to know the spatial location of other defects such as scratches, indentations, bumps and other irregularities in relation to the various layers of the wafer structure.
These are only a few examples of the types of puzzles that engineers must solve everyday to insure efficient, cost effective and quality wafer production.
Accordingly, there is a need to spatially resolve the location of defect that may reside in or on integrated circuit product devices or wafers.